1. Field of the Invention
The present invention relates generally to telecommunications network management. More particularly, the present invention relates to reducing undesirable phase transients caused by switchover during restoration from equipment failure in a telecommunications network.
2. Related Art
Modern telecommunication equipment has given network designers greater flexibility to create complex and diverse network topologies. In part, this flexibility is achieved by allowing designers to control selector switches in network equipment. The selector switches provide network equipment with the capability to select from among several different sources of communications signal inputs or outputs.
In general, each piece of network equipment has both an input selector switch and an output selector switch. The input selector switch selects one input from a plurality of inputs. The one input can, for example, provide a source of synchronization for the equipment. The output selector switch selects one output from a plurality of outputs on which to transmit a signal. The output can, for example, provide a synchronization source for another piece of network equipment. By appropriately choosing network selector switch placements, a network designer can design a network topology for network synchronization. The topology must meet various engineering requirements including traceability and loop-free design.
The selector switches are generally remotely programmable. Thus, the network topology can be changed after a network designer chooses an initial configuration. Moreover, using equipments having programmable selector switches allows a network management system to restore a network following a failure to a configuration that continues to adhere to the engineering requirements. This process is known as xe2x80x9cself-restoration.xe2x80x9d
To perform such xe2x80x9cself-restoration,xe2x80x9d the network controls replacement of a lost signal by setting the selector switch to a new position corresponding to a desired replacement signal. This process is known as xe2x80x9cswitchover.xe2x80x9d That is, the selector switch switches over from a position corresponding to the failed signal input to a position corresponding to the replacement signal input. In conventional systems, switchover is limited to switching between only two channels.
However, the xe2x80x9cswitchoverxe2x80x9d process often results in phase transients introduced into the signal being communicated. When the failed piece of equipment is repaired and put back into operation in the network, a second switchover occurs, wherein communication is routed through the repaired equipment, even though the temporarily used equipment is operational. This process is known as xe2x80x9creversion.xe2x80x9d Reversion occurs because the network sees the originally preferred signal has been placed back in the network. In conventional systems, the selector switch xe2x80x9crevertsxe2x80x9d back to the original setting.
However, reversion is generally undesirable when the communication signal is a synchronization signal. Where the signal is a synchronization signal, phase transients caused by switchover can lead to significant degradation in network performance. As a result, switchovers should be minimized to the extent possible. Network designers generally accept the risk associated with the switchover from the failed piece of network equipment. This is because the risk of performance degradation due to phase transients is acceptable relative to not having network access. However, reversion from the temporarily used equipment to the repaired equipment is not desirable where the two equipments are of substantially equal quality. Thus, what is required is a priority scheme for preventing undesirable switchover when a failed piece of equipment is repaired and placed back in a network. Moreover, the priority should provide sufficient flexibility to allow switching between more than two channels.
The present invention reduces undesirable switchover by introducing a novel priority scheme. A table of priorities, storing a priority for each of the selector source inputs for a selector switch, is created. Priorities are assigned such that selector sources, predetermined to be substitutes for one another, are equal. In this manner, when a first selector source is substituted for a second selector source, there is no reversion when the first selector source is repaired. This is because the priorities are equal. That is, the first selector source repair does not cause a reversion because its priority is not higher than that of the second selector source.
Moreover, using the priority scheme of the present invention allows network designers to control network topology. Because the selector switches in modern equipment are often programmable, a large degree of freedom is given network designers to access and modify the priority tables stored in a particular network equipment. Changing the selector source can result in changes to network topology.
The flexibility allowed by facilitating changes to network topology gives a network designer more control over network diversity. Diversity provides alternate paths for transmitting information between a particular source and destination equipment. Providing diverse paths gives robustness to the network design topology due to the ability of the network to route around failures in equipments or communications paths.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the digit(s) to the left of the two rightmost digits in the corresponding reference number.